The demand for heat-sensitive recording mediums has rapidly increased with the spread of thermal heads in recent years. Magnetic information is often displayed as visible information on prepaid cards which are rapidly spread in the fields of communication, transportation, distribution, etc, in particular. Such magnetic cards are widely used as highway cards, prepaid cards in department stores, supermarkets, etc., and JR orange cards.
However, the area on which visible information can be displayed is limited to only a part of the recording medium. For example, when the balance is recorded on a large denomination prepaid card, the case occurs that information is no more displayed. In this case, a new card is conventionally reissued. Accordingly, there is a problem that costs are increased.
Studies have been made to provide a reversible recording medium which enables recording and erasing to be repeatedly conducted on the same area to overcome the above-described problem. When the recording medium is used, previous unnecessary information can be erased, and new information can be displayed. Accordingly, it is not necessary that a new card is reissued when display is no more made. Further, when the recording medium is used as, for example, facsimile paper, resources can be saved, and the recording medium can contribute to the solution of environmental problems.
As the heat-sensitive recording mediums which enable the recording and erasing of information to be reversibly conducted, there have been conventionally proposed those having a heat-sensitive layer formed by dispersing an organic low molecular weight material such as a higher alcohol or a higher fatty acid in a resin matrix such as polyvinyl chloride, a vinyl chloride-vinyl acetate copolymer, a polyester or a polyamide (see, JP-A-54-119377 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-55-154198 and JP-A-2-1363).
The principle of forming an image on the reversible heat-sensitive recording medium and erasing it therefrom is based on that the transparency of the heat-sensitive layer is different when the temperature of the heat-sensitive layer is raised to a different temperature, and restored to room temperature. Namely, when the temperature of the above-described recording medium is elevated to a predetermined temperature and then restored to room temperature, the recording medium shows a transparent state, while when the temperature thereof is elevated to a different temperature and then restored to room temperature, the recording medium shows an opaque state.
It is preferred that recording on the above-described heat-sensitive recording layer is made by a thermal head. It is preferred that erasing is made by a heated roll, a hot stamp or a thermal head.
However, when the use of general-purpose recording device is taken into consideration, it is preferred that erasing is made by using a thermal head. In this case, when the recording medium disclosed in JP-A-55-154198 are used, an erasable proper energy range is extremely narrow, and hence erasing cannot substantially be made.
JP-A-2-1363 proposes that the erasable energy range is widened by adding a high melting material as the second component for the organic low molecular weight material to overcome the above-described problem.
However, the recording medium has a problem that the apparent melting point of the high melting material is lowered and as a result, an erasable energy range cannot be sufficiently widened.
The present inventors have eagerly made studies to overcome the above-described problems and found that when a material capable of imparting orientation to the melt of a predetermined organic low molecular weight material is blended with the low molecular weight material, the above-described problems can be overcome. The present invention has been accomplished on the basis of this finding.